New evidence of environmental advantages of geopolymer use – may reduce emissions causing global warming significantly compared to conventional concrete
Geopolymers, which have been created to replace cement, are not in all cases more environmentally sustainable than conventional concrete. However, LUT University's recent study on geopolymer composite recipes revealed significant potential for environmental advantages.
Concrete is the world's most frequently used construction material, and the cement that its manufacture requires produces roughly 8% of the world's carbon dioxide emissions. Geopolymers – cement-like binders created as a reaction of mineral by-product flows and alkaline activators – are a rising trend in research that is hoped to reduce construction industry emissions.
Geopolymer composites are created as a combination of a selected geopolymer, sand and gravel, resulting in a concrete-like construction material. LUT has studied the environmental impacts of fibre-reinforced geopolymer composites manufactured with different compositions. The assessment of environmental impacts covered, for instance, impacts on global warming, the amount of non-renewable natural resources, and ecotoxicity potentials.
The study examined binder recipes that contained coal fly ash created as an industrial by-product, or a mix of fly ash and blast furnace slag. The recipes were meant for the manufacture of products reinforced with steel, glass fibre or polypropylene.
The study examined a total of 24 recipes, which were obtained from previous geopolymer composite studies and were of equivalent strengths. At the end of the study, the binder recipes with the most beneficial environmental impacts were compared to conventional concrete.
The outcome of the study was that the climate impact of the best fibre-reinforced geopolymer composite had a nearly 60% lower global warming intensity than steel-reinforced concrete.
In contrast, emissions harmful in terms of natural resource consumption varied greatly. "For the three geopolymer recipes studied, the emissions were, at their worst, 26% higher, and at their best, 51% lower than those of steel-reinforced concrete," states Researcher Mariam Abdulkareem.
Abdulkareem goes on to say that at the final stages of the research, all environmental impacts were compounded to achieve a so-called normalised result.
"Our results indicate that the environmental impacts of fibre-reinforced geopolymer composites were overall 19–37% lower than those of steel-reinforced concrete."
New recipes for boosting the use of industrial mineral wastes
Environmental assessments that take the impacts of the entire life cycle into account provide important information on the further development of the materials. According to Professor Mika Horttanainen from LUT's Sustainability Science department, the manufacture of alkaline activator chemicals turned out to contribute the most to environmental impacts.
"The development of new geopolymers should aim for recipes with as small an amount of alkaline activators as possible," relates Horttanainen.
LUT's geopolymer research is part of the EU-funded Urban Infra Revolution (UIR) research project. The project develops construction materials and related manufacturing methods, equipment and business models that utilise local South Karelian industry by-product flows.
In addition to having lower greenhouse gas emissions than cement, geopolymer composites provide a potential means to boost the utilisation of mineral waste.
The current recipes are based primarily on coal ash and blast furnace slag, which are already partly utilised by-products. However, the UIR project develops recipes also for other industrial mineral wastes, which are created in large amounts around the world," concludes Horttanainen.
The Urban Infra Revolution (UIR) research project, coordinated by the City of Lappeenranta, will continue until autumn 2020.
Research article (open access):
Abdulkareem et al. 2019. How environmentally sustainable are fibre reinforced alkali-activated concretes? Journal of Cleaner Production, 231 https://doi.org/10.1016/j.jclepro.2019.07.076